The present invention relates to a radio communication system, and further relates to primary and secondary stations for use in the system and to a method of operating the system. While the present specification describes a system with particular reference to the emerging Universal Mobile Telecommunication System (UMTS), it is to be understood that such techniques are equally applicable to use in other mobile radio systems.
In a radio communication system it is generally required to be able to exchange signalling messages between a Mobile Station (MS) and a Base Station (BS). Downlink signalling (from BS to MS) is usually realised by using a physical broadcast channel of the BS to address any MS in its coverage area. Since only one transmitter (the BS) uses this broadcast channel there is no access problem.
In contrast, uplink signalling (from MS to BS) requires more detailed considerations. If the MS already has an uplink channel assigned to it, for voice or data services, this signalling can be achieved by piggy-backing, in which the signalling messages are attached to data packets being sent from the MS to the BS. However, if there is no uplink channel assigned to the MS piggy-backing is not possible. In this case a fast uplink signalling mechanism may be available for the establishment, or re-establishment, of a new uplink channel.
In many systems, for example those operating to the Global System for Mobile communication (GSM) standard, fast uplink signalling is enabled by the provision of a random access channel using a slotted ALOHA or similar protocol. However, such a scheme works satisfactorily only with a low traffic load, and is not believed to be capable of handling the requirements imposed by third-generation telecommunications standards such as UMTS.
To meet these requirements one UMTS embodiment includes a dedicated signalling channel, which comprises frames including a time slot for each MS registered with the controlling BS. If a MS requires a service from the BS it transmits a request in its allocated slot then waits for an acknowledgement from the BS setting up the required service. Some advantages of such a scheme are that the signalling is more efficient than with a random access channel, as there is no transmission of a large message; and that there is no risk of collisions, as each MS is allocated a unique time slot.
However, the provision of a dedicated signalling channel also has some disadvantages. The complexity of a hardware implementation is increased, because of the need for additional code generators in the MS and additional matched filters in the BS. The complete system is also made more complicated because of the inclusion of another type of transport channel.
An object of the present invention is to alleviate the disadvantages of providing a dedicated signalling channel while retaining its advantages.
According to a first aspect of the present invention there is provided a radio communication system comprising a primary station and a plurality of secondary stations, the primary station having means for partitioning a single uplink transmission channel between random access and dedicated signalling transmissions from the secondary stations and means for allocating a time slot for a dedicated signalling transmission by a secondary station.
According to a second aspect of the present invention there is provided a primary station for use in a radio communication system, wherein means are provided for partitioning a single uplink transmission channel between random access and dedicated signalling transmissions from secondary stations, and for allocating a time slot for a dedicated signalling transmission by a secondary station.
According to a third aspect of the present invention there is provided a secondary station for use in a radio communication system in which a single uplink transmission channel is partitioned between random access and dedicated signalling transmissions and time slots are allocated for dedicated signalling transmissions by secondary stations, wherein means are provided for transmitting random access and dedicated signalling transmissions in the allocated portion of the channel.
According to a fourth aspect of the present invention there is provided a method of operating a radio communication system comprising a primary station and a plurality of secondary stations, the primary station partitioning a single uplink channel between random access and dedicated signalling transmissions from the secondary stations and allocating a time slot for a dedicated signalling transmission by a secondary station.
The present invention is based upon the recognition, not present in the prior art, that a random access channel and a dedicated signalling channel can be combined into a single physical channel using the same hardware for both access mechanisms.